<meta charset="utf-8">
(#) Data tags should only declare unique attributes

!!! WARNING: Data tags should only declare unique attributes
   This is a warning.

Id
:   `IntentFilterUniqueDataAttributes`
Summary
:   Data tags should only declare unique attributes
Severity
:   Warning
Category
:   Correctness
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   7.1.0 (January 2022)
Affects
:   Manifest files
Editing
:   This check runs on the fly in the IDE editor
See
:   https://developer.android.com/guide/components/intents-filters
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/AppLinksValidDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/AppLinksValidDetectorTest.kt)

`<intent-filter>` `<data>` tags should only declare a single unique
attribute (i.e. scheme OR host, but not both). This better matches the
runtime behavior of intent filters, as they combine all of the declared
data attributes into a single matcher which is allowed to handle any
combination across attribute types.

For example, the following two `<intent-filter>` declarations are the
same:
```xml
<intent-filter>
    <data android:scheme="http" android:host="example.com" />
    <data android:scheme="https" android:host="example.org" />
</intent-filter>
```

```xml
<intent-filter>
    <data android:scheme="http"/>
    <data android:scheme="https"/>
    <data android:host="example.com" />
    <data android:host="example.org" />
</intent-filter>
```

They both handle all of the following:
* http://example.com
* https://example.com
* http://example.org
* https://example.org

The second one better communicates the combining behavior and is clearer
to an external reader that one should not rely on the scheme/host being
self contained. It is not obvious in the first that http://example.org
is also matched, which can lead to confusion (or incorrect behavior)
with a more complex set of schemes/hosts.

Note that this does not apply to host + port, as those must be declared
in the same `<data>` tag and are only associated with each other.

!!! Tip
   This lint check has an associated quickfix available in the IDE.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
AndroidManifest.xml:5:Warning: Consider splitting data tag into multiple
tags with individual attributes to avoid confusion
[IntentFilterUniqueDataAttributes]
    &lt;data alt-android:scheme="https" alt-android:host="example.com"/&gt;
    -----------------------------------------------------------------
AndroidManifest.xml:6:Warning: Consider splitting data tag into multiple
tags with individual attributes to avoid confusion
[IntentFilterUniqueDataAttributes]
    &lt;data alt-android:scheme="http" alt-android:host="example.org"/&gt;
    ----------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`AndroidManifest.xml`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers
&lt;manifest xmlns:alt-android="http://schemas.android.com/apk/res/android"
    package="com.example.helloworld" &gt;
    &lt;activity alt-android:name="com.example.Activity"&gt;
        &lt;intent-filter&gt;
            &lt;data alt-android:scheme="https" alt-android:host="example.com"/&gt;
            &lt;data alt-android:scheme="http" alt-android:host="example.org"/&gt;
        &lt;/intent-filter&gt;
    &lt;/activity&gt;
&lt;/manifest&gt;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/AppLinksValidDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Adding the suppression attribute
  `tools:ignore="IntentFilterUniqueDataAttributes"` on the problematic
  XML element (or one of its enclosing elements). You may also need to
  add the following namespace declaration on the root element in the
  XML file if it's not already there:
  `xmlns:tools="http://schemas.android.com/tools"`.

  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;manifest xmlns:tools="http://schemas.android.com/tools"&gt;
      ...
      &lt;activity tools:ignore="IntentFilterUniqueDataAttributes" .../&gt;
    ...
  &lt;/manifest&gt;
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="IntentFilterUniqueDataAttributes" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'IntentFilterUniqueDataAttributes'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore IntentFilterUniqueDataAttributes ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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